Drive gear construction



Sept. 21, 1965 N. B. SHIMP 3,206,996

DRIVE GEAR CONSTRUCTION Filed Dec. 27, 1961 \LZI MBI-NVLII; .P

United States Patent M 3,206,996 DRIVE GEAR CONSTRUCTION Nathan B. Shimp, Celina, Ohio, assignor to Speicher Brothers, Inc., Celina, Ohio, a corporation of Ohio Filed Dec. 27, 1961, Ser. No. 162,521 1 Claim. (Cl. 74-460) This application is a continuation-in-part of abandoned application Serial No. 609,895 filed September 14, 1956.

This invention relates to gear construction and primarily to the construction of the drive gear in a trenching machine, which is designed to operate a digging wheel therein and thereby cooperate with the gear carried by said digging wheel.

In trencher construction of the class to which this invention is directed, the digging wheel is a large diameter unit, upon which a series of digging elements or buckets are suitably mounted, the entire digging wheel being supported upon a framework, which framework is in turn carried by a body and suitably manipulated to raise and lower the same to dig ditches or trenches of greater or less depth.

In the construction of the trencher here under consideration, the digging wheel is provided with an internal gear, of very large diameter, and a suitably arranged supporting structure whereby the wheel is carried at three points, two of the same being idler Wheels and the gear providing the third point, that is the drive gear in conjunction with the internal gear of the digging wheel.

In view of the construction herein outlined, a large portion of the support of the digging heel is directed through the drive gear to the framework upon which the drive gear and its associated mechanism is mounted. It will therefore be understood that the wear factor of the internal gear in conjunction with the drive gear is different in large measure from that which exists with reference to gears having fixed axes and thereby a fixed relationship independent of the weight of the respective mechanisms with which the gear parts are associated.

The trencher herein under consideration as to the gear construction thereof, involves the novel form of drive gear wherein wear which results from rotation of the digging wheel by the drive gear and the weight of the digging wheel carried by the drive gear, is compensated for and is not permitted to affect the driving operation of the drive gear because of the novel construction thereof as will be subsequently set forth.

It is a particular object of this invention to construct a drive gear with teeth thereof for meshing engagement with an internal gear of a trenching or digging wheel, in such a manner as to permit normal wear to take place, prevent the wear from in turn developing a protuberance or hump at the roots of the gear teeth as would ordinarily be the case where the gear teeth are constructed in the normal manner and expected to operate likewise.

A particular object of the invention is to provide gear teeth on the drive gear which are undercut at the roots thereof, in such a manner as to obviate the development of a hump or bump near said roots in the ordinary course of operation as wear takes place.

A more particular object of this invention is to provide a gear tooth which is provided with a soft core and a hardened surface, the proportions of the tooth in respect to width and height or outward extension thereof being such that the undercut portion of the gear tooth is never contacted by the meshing gear tooth and the combination of hardened surface on the drive gear tooth with a nor mal untreated surface of the driven gear is such as to provide increased advantage in gear construction for the purposes herein.

A further object of the invention is to provide gear teeth 3,206,996 Patented Sept. 21, 1965 which are of somewhat conventional form generally speaking except that the connection of the gear teeth with the body of the gear itself includes a relatively soft extension of the gear body, on the surface of which extension and which provides the tooth and driving engagement, is a hardened area, all for the purpose of increasing the life of the respective gears and particularly the teeth thereof.

A more particular object of the invention is to provide a drive gear in which the body thereof is formed of cast steel of a given specification, and the teeth are formed so that the surfaces thereof are provided with a hardened area and a core in each tooth is of softer form corresponding to that of the body, each individual tooth is undercut at its root or juncture with the body of the gear, the undercut extending approximately the depth of the hardened section, the hardened area being arranged to engage with mating teeth of a corresponding gear driven by the gear aforesaid.

Other and further objects of the invention will be understood from a consideration of the specification and drawing attached hereto wherein:

FIGURE 1 is a side elevational view of a trencher embodying the construction hereof, and illustrating the general arrangement of the gear parts.

FIGURE 2 is an enlarged fragmentary section of the digging wheel and its supporting associated frame, to further illustrate the manner of engagement of the drive and driven gears.

FIGURE 3 is a greatly enlarged fragmentary view showing the engagement of the drive and driven gears and illustrating further certain wear conditions which may ordinarily take place.

FIGURE 4 is a sectional view showing the drive gear.

FIGURE 5 is an enlarged fragmentary sectional view showing the construction of the drive gear as to the tooth formation and hardened areas thereof.

Referring now to FIGURE 1, a trencher is shown as comprising a supporting vehicle such as 1 having the front wheels 2, rear wheels 3, engine 4 and associated gearing 5 operated by the engine, the gearing 5 in turn transferring through suitable chain drives such as 6 and 7 in rotary motion to a sprocket 8, the sprocket 8 being mounted on a shaft 9, the shaft 9 in turn transmitting to a drive gear 10, the necessary drive rotation for the dig ging wheel generally illustrated at 11.

The digging wheel 11 includes the digging buckets 12 mounted on the periphery thereof and a suitable construction to support such buckets 12, the entire wheel being carried by the frame 13 which includes a generally triangular section at one corner of which is mounted an idler wheel 14, a further idler wheel 15a being located at another corner, the gear 10 providing the third point of support and being in engagement with an internal gear 15 more particularly disclosed hereinafter and being attached to a member upon which the digging buckets 12 are carried.

The frame 13 is connected with a further frame unit 16 which is adapted to be raised and lowered by cables 17 and pivoting about a point 18 on a support frame 19 mounted on the vehicle 1.

Referring now to FIGURE 2, the internal gear 15 is provided of any preferred form and usually cast in segments, although it could be made in a single unit if desired, the segmental construction being preferable so as to minimize replacement costs when wear takes place or breakage occurs.

The gear teeth formation is more particularly illustrated in FIGURE 3, these gear teeth being denoted 20 and of generally frusto-conical form, and arranged to engage with the teeth of the drive gear 10, the teeth of this latter gear being those particularly under consideration here as to the construction thereof.

In order to illustrate the problem which this invention solves, the FIGURE 3 disclosure is referred to and illustrates the teeth 21 of the drive gear as being generally frusto-conical like the teeth 20 so as to interengage therewith, the teeth in this instance however being provided with undercuts at the roots thereof, these undercuts being denoted 22, and for the purposes hereinafter set forth.

In order to particularly explain the advantages derived by this invention, it will be noted that as illustrated in FIGURE 3, dotted lines 23 are indicated as extending from the undercut to the tip of the tooth in each case, this dotted line indicating the normal wear condition which exists, and which takes place in ordinary gear construc- 1 sequently set forth. Of course this protuberance will not form as quickly as would otherwise be the case in normal gears which do not have the undercut area since the wear would take place down through the surface of the tooth and extend beyond what is the undercut as illustrated forming a bump there as will be readily understood.

This undercut 22 in each case is of limited extent and is only of small radial extent as well as reducing the circumferential width of the tooth at its root by only a sufiicient amount to obviate the development of the bump or protuberance previously suggested.

The drive motion of the drive gear of FIGURE 3 will be in the direction of the arrow 24 for example and thus the wear taking place would be as indicated by the dotted lines 23. Obviously if the drive direction were reversed,

a reverse condition would exist and the dotted lines 25 i would represent the wear condition.

Turning more particularly to the actual tooth construction, FIGURE 5 is referred to, and illustrates the body of the gear 10 as being formed of an integral casting, preferably SAE-4145, a heat treatable cast iron, the teeth being illustrated as'including a core portion 28 of generally triangular form and a hardened section 30 which extends over and is of course integral with the core, the general formation being only susceptible of illustration and no exact line of demarcation being present as will be readily understood because of the fact that this gear is hardened by induction hardening to 55 or 60 Rockwell C. The line of demarcation indicated as involving the unheat treated portion of the tooth is only general and intended to indicate that there is a definite core inthe tooth which is not heat treated and a hardened surface which is, the hardened area terminating at the undercut 22 generally.

The circumferential width of the core 28 is about the extent from the undercut at one side of the tooth to the undercut at the other, and the outward extent substantially two-thirds to three-quarters the height or radial length of the tooth in each case.

From the foregoing it will be understood that all of the teeth of the drive gear are hardened with generally the same hardened surface so that the wear conditions which may take place will be very materially reduced as to the time element and since the teeth of the internal gear 15 are not hardened but are as cast, an ideal wear arrangement is provided particularly since the digging wheel 11 is supported by the drive gear in part and thus provides a substantially different type of wear problem than is existent in the normal tooth construction of fixed center gears.

While the drive gear 10 as shown in FIGURE 4 is provided with a shoulder 32 which carries a portion-of the load of the digging wheel, the rate of wear of the shoulder portion 32 is different from the teeth in the normal gear construction and thereby the bump condition is emphasized in such prior known devices. Thehardened areas of the teeth as illustrated herein and described, make possible substantially longer life before it is necessary to rebuild .or otherwise reconstruct the drive gear arrangement and substituting new gears or replacement parts therefor. Another destructive factor which this gear construction obviates is the shock to the teeth when an obstruction is encountered since the teeth of the drive gear are heat treated to embody a strong, but not britle core, such shock is less likely to break a tooth or otherwise damage the drive gear.

I claim:

In a drive gear for a trencher the combination comprising a gear body, a plurality of shock absorbing gear teeth extending outwardly from said body, each of said gear teeth including a substantially triangular core portion and a substantially cup-shaped hardened surface portion, said cup-shaped hardened surface portion extending partially over said core and terminating at a point above the interconnection of said core and said gear body to, define an undercut, said hardened portion including a relatively thick extremity with side portions of diminishing thickness, each of said gear teeth thereby having a base of reduced circumference than the circumference of said tooth at a point where said hardened portion voverlies said core portion.

References Cited by the Examiner UNITED STATES PATENTS 42,605 5/64 Skaats 74-462 2,051,915 8/36 Sykes 74-460 2,220,419 11/40 Meldahl' 74-462 2,279,216 4/42 Way 74-460 2,306,854 12/42 Zimmer 74-462 2,829,724 4/58 Burns et al. 2,834,125 5/58 Brant 37-97 2,905,011 9/59 Armstrong et al.

OTHER REFERENCES Metal Progress, December 1944 (pages 1263-1267).

DON A. WAITE, Primary Examiner. 

